Altered 5-HT metabolism in the lung appears to be an early event in acute pulmonary failure secondary to endothelial cell damage, and may be detected by an increase in the level of free 5-HT in pulmonary blood. Direct and unambiguos measurement of free blood 5-HT levels to obtain early diagnosis of pulmonary damage would be possible with electro-chemical methodology if an electrode of adequate specificity and sensitivity were available. The proposed research will investigate the feasibility of developing a specific electrochemical sensor for 5-HT consisting of an electrode derivatized with antibody to 5-HT. An antibody to 5-HT will be immobilized on electrode surfaces by covalent bonding or chemisorption. The antibody-derivatized electrode (Ab-electrode), when exposed to a solution (e.g., blood, plasma, CSF, etc.) containing 5-HT, may react only with 5-HT to produce an electrochemically measurable immune complex on the electrode surface. The Ab-electrodes will be evaluated with respect to: (1) the potentiometric and voltametric response of the Ab-electrodes to 5-HT; (2) the sensitivity and selectivity of the electrod response to 5-HT; and (3) the ability of the derivatized electrode to detect and quantify 5-HT in whole blood, plasma, or serum. Agreement between electro-chemical and fluorometric measurements of 5-HT in plasma and serum will constitute a demonstration of the ability of an Ab-electrode to measure 5-HT directly in blood. The successful completion of the overall project, including Phase II, will make available for the first time technology for performing rapid, real time analysis of 5-HT without the need for sample manipulation, extraction, or radiolabelled reagents. The availability of specific electrodes for 5-HT may yield diagnostic methodology for the clinical assessment of pulmonary endothelial cell function, thromboembolic disease, platelet viability following storage or infusion, as well as any of the other physiological or pathological states in which 5-HT is implicated. The method of analysis is not limited to 5-HT, but can be extended to include any compound to which an antibody can be prepared, e.g., 5-HT metabolites or other bioactive compounds. The electrodes to be developed could form the basis for new diagnostic or patient monitoring instrumentation for use in hospitals, clinical laboratories, physicians' offices, or even at home by the patient.